Drive for a balance in an electric timepiece



Dec. 2, 1969 YOSHIKIYO FUTAGAWA ET 3,481,133

DRIVE FOR A BALANCE IN AN ELECTRIC TIMEPIECE 4 Sheets-Sheet 1 Filed May8, 1967 /2a 7125 /Zc F l 6 2 INVENTORS YOSHIKIYO FUTAGAWA CHIAKI KOMATSU64%, ATTORNEYS 1969 YOSHIKIYO FUTAGAWA ET AL 3,431,138

DRIVE FOR A BALANCE IN AN ELECTRIC TIMEPIECE Filed May 8, 1967 4Sheets-Sheet 2 INVENTORS YOSH IKIYO F UTAGAWA CHIAKI KOMATSU ATTORNEYS1969 YOSHIKIYO FUTAGAWA ET AL 3,481,138

DRIVE FOR A BALANCE IN AN ELECTRIC TIMEPIECE Filed May 8, 1967 4Sheets-Sheet 5 FIG.6

INVENTORS YOSHIKIYO FUTAGAWA BY CHIAKI KOMATSU ATTORNEYS Dec. 2, 1969YOSHIKIYO FUTAGAWA ET AL. 3,481,138

DRIVE FOR A BALANCE IN AN ELECTRIC TIMEPIECE Filed May 8. 1967 4Sheets-Sheet 4 FIG. 9A A?! E AC 1, r i I FIG 9s 0 J l FIG. 96 E FIG/0AFIGJOB E+Z/ m V QK' R l I T t 5 I A i B I I i A too a 004 a, :0 at

INVENTORS YOSHIK FUTAGAWA BY CHIAKI MATSU V TTORNEYS United StatesPatent 3,481,138 DRIVE FOR A BALANCE IN AN ELECTRIC TIMEPIECE YoshikiyoFutagawa and Chiaki Komatsu, Suwa-shi, Japan, assignors to KabushikiKaisha Suwa Seikosha, Ginza-Nishi, Chuo-ku, Tokyo, Japan Filed May 8,1967, Ser. No. 636,735 Claims priority, application Japan, May 10, 1966,41/29,296 Int. Cl. G04c 3/04 US. CI. 5828 6 Claims ABSTRACT OF THEDISCLOSURE An electric timepiece is provided having an oscillatorcircuit which provides a pulse output which facilitates selfexcitedoscillation of the balance wheel and control of the balance oscillation,in an electromechanical transducer wherein the balance wheel is engagedonly near the center of the balance oscillation by an anchor and isarrested at a stable point during this engagement of the balance Wheel.The oscillator circuit provides a large amount of energy to the balancewheel at the start of the balance oscillation period than the energyapplied thereto in the stable state of oscillation, by providing anelectrical pulse having a pulse width which is wider at the start of thebalance oscillation than in the stable state of oscillation. Theamplitude of the balance oscillation is controlled by having the outputenergy of the electromechanical transducer be a function of theamplitude of the balance oscillation.

The present invention relates to an electric timepiece, and moreparticularly to an electric timepiece utilizing an oscillator circuitfor driving the electric timepiece whereby the pulse output of theoscillator enables self-excited oscillation and amplitude control of thebalance Wheel, with the electromechanical transducer employed fordriving the balance wheel engaging the balance wheel only near thecenter of the balance oscillation and rendered stationary at a stablepoint during the oscillation.

In electric timepieces, e.g., Wristwatches, it is desired that in orderto maintain synchronisrn, that the balance wheel itself does notconstitute an element of the transducer, and accordingly, there isprovided an anchor operative with an electromechanical converter.

In such electric timepieces, it is desired to decrease the moment ofinertia of the anchor which has a permanent magnet, and to make itsconstruction relatively simple. Furthermore, in order to prevent leakageof magnetic flux in the magnetic circuits, the yoke is commonly disposedvery close to the permanent magnet. However, in such instances, thepermanent magnet is required to overcome a peak of potential energy dueto the variations in permeance of the magnetic circuit. Accordingly, itis necessary to supply a sufficiently large force to the balance wheelat the start of the oscillation period, when the balance wheel is at thestationary state and has no stored energy, while the aforementionedenergy peak is effective to prevent the anchor from abnormal vibrationwhich may be caused by outer disturbances when the balance wheel isoscillating.

Thus, it is desired to supply a large amount of energy to the balanceWheel only at the start of the oscillation, and a small amount of energythereto sufficient to maintain the balance oscillation when the balancewheel is in the stable state of oscillation. If this is not done, thebalance wheel is subject to a phenomena known as knocking.

'ice

It is accordingly an object of the present invention to provide anelectric timepiece having a transducer, wherein a relatively largeamount of energy is applied to the balance wheel at the start of theoscillation period and a reduced amount of energy is applied thereto inthe stable state of oscillation.

Another object of the present invention is to provide an electrictimepiece comprising an oscillator circuit which has a reduced powerconsumption in the stable state of oscillation while maintainingself-excited oscillation of the balance wheel.

A further object of the present invention is to provide an electrictimepiece having an oscillator circuit which supplies to the transducer,pulses having a larger pulse width at the start of the balanceoscillation than the pulse width in the stable state of oscillation.

Yet, another object of the present invention is to provide an electrictimepiece wherein the amplitude of the balance oscillation isautomatically controlled by the output energy of the transducer.

In accordance with the principles of the present invention, there isprovided an electric timepiece having an oscillator circuit whereby thetransducer which drives the balance wheel and detects the motion thereofnear the center of the oscillation period, with the transducer engagingthe balance Wheel and increasing its rotative force. Furthermore, thereis supplied to the transducer an electric pulse having a Wide pulsewidth at the start of the balance oscillation and a pulse of narrowwidth when the balance wheel is in the stable state of oscillation, tothereby allow the balance wheel to overcome a peak of energy at thestart of the oscillation period.

The novel features believed to be characteristic of this invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and advantages thereof, maybest be understood by reference to the following description taken inconnection with the accompanying drawings wherein:

FIG. 1 depicts an electromechanical time piece transducer formaintaining balance oscillations in an electric timepiece which may beutilized with the novel oscillator of the present invention.

FIG. 2 shows the electromechanical transducer of FIG. 1 including themagnetic circuits set up therein.

FIG. 3 is a graphical representation of the variation of potentialenergy of the permanent magnet in the transducer shown in FIG. 1, withvariation in the rotary angular position of said permanent magnet.

FIG. 4 is a schematic circuit depiction of a conventional oscillatorutilized for driving the electromechanical transducer of FIG. 1.

FIG. 5 is a schematic circuit depiction of an oscillator in accordancewith the principles of the present invention, in one embodiment thereof.

FIG. 6 is a schematic circuit depiction of an oscillator in accordancewith the principles of the present invention, in a second embodimentthereof.

FIG. 7 is a schematic circuit depiction of an oscillator in accordancewith the principles of the present invention, in a third embodimentthereof.

FIG. 8 is a schematic circuit depiction of an osecillator in accordancewith the principles of the present invention, in a fourth embodimentthereof.

FIG. 9A is a waveform diagram of the induced voltage generated in thedriving coil and detecting coil of the electromechanical transducer ofFIG. 1.

FIG. 9B is a Waveform diagram of the voltage on the collector oftransistors 24 in the embodiments of FIGS. 5-8.

FIG. 9C is a waveform diagram of the voltage on the base of thecontrolling transistor in the embodiments of FIGS. 5 to 8. 1

FIGS. 10A is a waveform diagram of the variation in voltage with time onthe charging condenser in the embodiments of FIG. 5-8.

FIG. B is a waveform diagram of the variation in current with time inthe charging condenser of the embodiments of FIGS. 5-8.

Referring to FIG. 1, an electromechanical transducer for maintaining thebalance oscillation is shown to comprise a balance wheel 1, oscillatingabout its axis 2, and impulse pin 3 mounted on balance wheel 1,including an anchor 4 connected to its arbor 5. The balance wheel systemof FIG. 1 is thus seen to comprise many of the standard components foundin known mechanical watches.

A permanent magnet 6 having north and south magnetic poles 7 and 8respectively has rigidly connected thereto to anchor 4. A yoke 11 isprovided having magnetic poles 9, 9, 10, 10 to provide a magneticcircuit surrounding permanent magnet 6. As shown in FIG. 1, magneticpole 9 is disposed opposite to the north pole 7 of permanent magnet 6with pole 10 disposed opposite to the south pole 8 of permanent magnet6. A driving coil 12 having input terminals 12a, 12b, and 12c, is woundabout arm 11a of yoke 11, and detecting coil 13, having output terminals13a and 13b is wound about arm 11b of yoke 11. Driving coil 12 anddetecting coil 13 may be connected so the magnetic fiux through the yoke11 generated by each are added, by connecting terminal 12c and terminal13a and providing a current path from terminal 12a or terminal 13b.Although not shown in FIG. 1, a well known mechanism for driving thetrainwheel of the timepiece may be utilized for the anchor 4.

The operation of the electromechanical transducer of FIG. 1 is asfollows. Permanent magnet 6 is repulsed by magnetic poles 9 and 10 andis attracted by magnetic poles 9 and 10, whereby there is appliedthereto a rotative moment to cause rotation if the current pulse appliedto the driving coil is sufficiently Wide to generate the magnetic fluxpattern as show by the solid line arrows in yoke 11 in FIG. 1.

When anchor 4 engages impulse pin 3 the moment of balance wheel 1 addsto its force, and if a large enough force is applied to anchor 4,balance Wheel 1 leaves anchor 4, while permanent magnet 6 moves from thedirection of magnetic poles 9, 10' to the direction of magnetic poles 9and 10 and is stationary there. Due to the restorative force of the hairspring, the balance wheel shortly thereafter takes its original positionto again engage with anchor 4 near the center of oscillation of balancewheel 1, with permanent magnet 6 then returning to the position ofstability i.e. from the direction of magnetic poles 9 and 10, to that ofmagnetic poles 9 and 10', due to the conservative energy of balancewheel 1.

If thereafter, driving coil 12 has applied thereto a driving currentwhich generates a magnetic flux opposite in direction to the previousmagnetic flux direction, permanent magnet 6 is repelled to the oppositedirection by magnet poles 9 and 10, and is attracted by magnetic poles 9and 10', which accelerates the rotative moment of magnet 6 to add forceto the rotative moment of balance wheel 1 to take the original position,i.e. in the direction of magnetic poles 9 and 10'. Accordingly, by

providing an alternating current to driving coil 12 in synchronism withthe period of balance wheel 1, the added force is applied to balancewheel 1 and it reaches its usual amplitude when the lost energy is equalto the supplied energy. Permanent magnet 6 is rotated by virtue of themoment applied by the driving current and the conservative energy ofbalance wheel 1, whereby the magnetic flux flowing from north pole 7 tosouth pole 8 of permanent magnet 6 is switched from the solid line fluxlines of FIG. 1 to the dotted line flux lines of FIG. 2. Thus, thedirection of the flux lines is changed from the magnetic circuit runningfrom north pole 7, through magnetic pole 9, yoke 11, magnetic pole 10'to south pole 4 8, to the direction shown by dotted line in FIG. 2, i.e.from north pole 7 through magnetic pole 9', yoke 11 and magnetic pole 10to the south pole.

Due to the change in magnetic flux in yoke 11, an induced voltage isgenerated in driving coil 12 and detecting coil 13, the direction of theinduced voltage being opposite to that of the driving current. If thedirection of the driving current is opposite to that of the inducedvoltage, the electro-magnetic energy is converted into mechanical energyand adds force to balance wheel 1. The above mentioned induced voltagealso acts as a synchronous signal for" the electric circuit of the timepiece in accordance with the present invention, with the width of theinduced voltage waveform corresponding approximately to the duration ofthe engagement of anchor 4 with impulse pin 3 of balance wheel 1. Thewaveform of the above mentioned induced voltage is shown in FIG. 9A,wherein the lower half of the Waveform is an induced voltagecorresponding to the rotation of permanent magnet 6 from the directionof magnetic poles 9 and 10' to the magnetic poles 9' and 10. The upperhalf of the waveform b is an induced voltage corresponding to therotation of the permanent magnet 6 from the direction of magnetic poles9 and 10 to the magnetic poles 9 and 10'. As the amplitude ofoscillation of balance wheel 1 is increased, the duration of engagementwith anchor 4 decreases, while at the same time the rotative velocity ofpermanent magnet 6 and the change of magnetic flux are increased,causing the induced voltage to be increased as shown by the dotted linewith respect to the solid line in FIG. 9A. It will be noted that withrespect to the balance wheel 1, as shown in FIG. 1, permanent magnet 6when united with anchor 4 makes the magnetic poles opposite to that ofnorth pole 7 and south pole 8 generate a magnetic force of inversepolarity, and is attracted and stands stationary in either direction ofmagnetic poles 9 and 10 or 9' and 10 during almost the complete periodof the balance oscillation. Accordingly, the relation to the tuningangle 0 of permanent magnet 6, and its magnetic potential energy isrepresented by the curve shown in FIG. 3, wherein -0 is the turningangle of the current magnet 6 when in the position of FIG. 1 it isstationary in alignment with magnetic poles 9 and 10, +0 correspondingto the turning angle of FIG. 2 wherein it is stationary and aligned withmagnetic poles 9 and 10, with 0 corresponding to the turning angle whenthe permanent magnet 6 is balanced by the attraction forces of magneticpoles 9 and 10, and 9 and 10, i.e. north pole 7 being situated near thecenter of the gap between magnetic poles 9 and 9' and south pole 8 beingequidistant between magnetic poles 10 and 10.

As shown in FIG. 3, there is a peak of magnetic potential energyoccurring within the turning angle of 20 of anchor 4. Accordingly in thestable state of oscillation of the balance wheel where the amplitude islarge, the conservative energy of the balance wheel must be sufficientlylarger than the value of the aforementioned peak of magnetic potentialenergy. In the stable state of oscillation, When balance wheel 1 movesanchor 4 and permanent magnet 6 through the angle of -0 to +0 balancewheel 1 loses energy in order to overcome the peak at angle 0 whenapproaching from the direction of 0 and conversely receives energy whengoing in the direction from angle 0 to angle +0 accordingly maintainingno loss of energy of the balance wheel 1. However, when the conservativeenergy of balance wheel 1 is smaller, at the beginning of oscillation,it will not have sufiicient momentum to overcome the aforementioned peakof magnetic potential energy and will stall. In order to overcome theaforementioned peak of energy, the transducer will require to haveapplied thereto an elec trical pulse of sufiicient height or Width.However, since the output voltage of the voltage source i.e. battery inan electric wrist watch is quite low, it is preferable to provide anoscillator circuit which can widen the width of the pulse, since it isgenerally difiicult to generate a pulse having a large amplitude.

If the anchor 4 of the transducer shown in FIG. 1, en-

gages the balance wheel during most of the oscillating period of balancewheel 1 at the start of the oscillation period, the oscillator circuitcan supply the additional force to the balance wheel 1 effectively toprovide an electrical pulse of sufiicient width to the transducer.However, as the amplitude of the balance wheel 1 reaches that of thestable state of oscillation, the duration of the engagement betweenbalance wheel 1 and anchor 4 is shortened, and accordingly even if theoscillator circuit provides a sufficiently wide electrical pulse to thetransducer, it will be of no avail, and accordingly it is necessary tonarrow the applied pulse width.

In FIG. 1, in order to add force to the balance wheel 1, the electricalcurrent flowing in driving coil 12 was alternating to generate analternating magnetic flux in yoke 11. However, if it is possible to addsufficient force to balance wheel 1 by means of a unidirectional drivingcurrent in driving coil 12, it will also be possible to maintain theoscillation of balance wheel 1 by having balance wheel 1 return to theposition where it drives anchor 4 by the conservative energy of balancewheel 1 to synchronize with the oscillation of balance wheel 1, i.e. theoscillator circuit may supply sufficient force to balance wheel 1 oncebalance wheel 1 has commenced its oscillatory motion. Hereafter, therewill be described various electrical oscillator circuits for providingan electrical pulse in synchronism with the period of the balanceoscillation for maintaining oscillation of the balance wheel. Suchoscillator circuits generally comprise a simple transistor amplifierhaving the transducer driving coil in the collector circuit and thedetecting coil in the base circuit, an astable transistor blockingoscillator having a time constant capacitor for controlling the periodof oscillation, together with a time constant resistor connected to thebase terminal of the transistor, or may include a monostable or astableoscillator circuit comprising a pair of transistors of similar oropposite polarity. It should be noted however that in the case of asimple amplifier, if the induced voltage in the detecting coil,generated by the balance oscillation is not sufficient, the transistorwill not be switched on, and it will be impossible to start the balanceoscillation from a stand still.

In such blocking oscillator circuits, the on time of the transistor i.e.the width of the pulse, is determined by the self inductance of thedriving coil and the detecting coil and the mutual inductance andresistance of these coils. Since the magnetic circuits in the transduceras shown in FIG. 1, are generally open in one part of the yoke, theinductance will be small and accordingly the width of the pulse will benarrow. It is noted that in such a transducer, the pulse width will bewidened if the ampli- 'tude of oscillation of the balance wheel isincreased, but it is impossible for such transducers to provide selfexcited oscillation.

In the aforementioned monostable oscillator circuits comprising a pairof transistors of the same polarity, the transistor also will not beswitched on without generating the induced voltage in the coils ashereinabove described. Also, in the case of the astable oscillators,even if the initial pulse width can be widened, to enable theoscillation to start from a stand still, the electrical powerconsumption will be disadvantageously substantially increased sinceeither of the two transistors will be switched on in the stable state ofoscillation.

As pointed out above, it is thus impossible for any of the conventionaloscillator circuits briefly described above, to provide the features ofself starting together with minimum power consumption. FIG. 4 shows sucha conventional oscillator having an astable oscillator circuit includinga pair of complementary transistors of opposite polarity, 15 and 16,with transistor 15 being used for driving and transistor 16 used forcontrolling. The negative induced voltage, as shown in FIG. 9A isgenerated in driving coil 17 in accordance with the motion of thebalance wheel, to render controlling transistor 16 on. By adding thisvoltage to controlling transistor 16, the timing circuit comprisingcharging condenser 18, and resistor 19, controlling transistor 16,resistor 21 and driving transistor 15 is thus rendered into the onstate. Once in the on state, the collector current of transistor 16which is also the base current of driving transistor 15 flowing throughresistor 21 renders driving transistor 15 on. When transistor 15 isrendered on, the collector voltage of transistor 15 drops drivingcontrolling transistor 16 further into the on condition by virtue of thepositive feed back action in this circuit. When driving transistor 15 isswitched on and is driven into the saturated condition, battery source23 provides a driving current to the driving coil opposing the inducedvoltage to supply energy to the balance wheel. The charging current ofthe aforementioned charging circuit comprising capacitor 18 and resistor19 flows from the positive terminal of battery 23 through the emitter tobase circuit of controlling transistor 16, resistor 19, chargingcapacitor 18, the collector to emitter circuit of driving transistor 15returning to the negative terminal of battery source 23, which chargingcurrent gradually decreases to sharply cut off controlling transistor 15and driving transistor 16 by virtue of the aforementioned positive feedback action.

In the aforementioned on state, if the discharge time constant ofcapacitor 18 is a little longer than the balance period, the circuitwill be switched on when the induced voltage is generated in accordancewith the motion of the balance wheel in the next moment. Accordingly, inthe conventional oscillator circuit shown in FIG. 4, it is possible tocontrol the transducer so as to supply sufficient energy which issynchronized with the period of the balance oscillation. However, thepulse width of the generated electrical pulse is determined by timeconstant capacitor 18 and charging resistor 19, i.e. the chargingvoltage added to capacitor 18 is only that of battery source 23, withthe final value of the charging voltage on capacitor 18 being the outputvoltage of battery source 23. Thus, in the case of adding force to thebalance wheel by means of the transducer as shown in FIG. 1, since it isimpossible to start the balance oscillation without providing asufficiently wide pulse at the start of the balance oscillation, thevalues of time constant capacitor 18 and resistor 19 are fixed in orderto widen the pulse width sufficiently for the oscillator circuit shownin FIG. 4. However, in such a case, even if the balance oscillation doesreach the stable amplitude, after disengagement of the balance wheel theoscillator circuit will supply the reactive electrical energy to thetransducer. In the case of the small batteries utilized in wristwatches, this action will shorten the battery life, and accordinglybecomes a very serious disadvantage in practical use. Diode 22, as shownin FIG. 4 functions to absorb the energy of the driving coil which is atthe trailing end of the electrical pulse.

Referring to FIG. 5, there is shown a first embodiment of an oscillatorcircuit in accordance with the principles of the present invention,wherein the above mentioned disadvantages of the conventional oscillatorcircuit of FIG. 4, and the like, are avoided. The oscillator of FIG. 5includes a positive feed back circuit comprising intermediary terminal12b of driving coil 12, detecting coil 13 as shown in FIG. 1, chargingcondenser 26, and charging resistor 27, the base to collector circuit ofcontrolling transistor 25, resistor 29, the base to collector circuit ofdriving transistor 24 and terminals and 12b of dr 1v ing coil 12, in theaforementioned sequence. A charging circuit for time constant capacitor26 is seen to compnse the positive terminal of battery source 31,emitter to base circuit of controlling transistor 25, resistor 27, timeconstant capacitor 26, detecting coil 13, intermediate terminals 12b and12c of driving coil 12, the collector to emitter circuit of drivingtransistor 24, and the negative terminal of battery source 31 in theaforementioned order. A discharge circuit is seen to comprise thepositive terminal of battery source 31, terminal 12a of driving coil 12,intermediate terminal 12b, detecting coil 13, time constant capacitor26, resistor 27, time constant resistor 28 (which provides a period ofoscillation a little longer than that of the balance wheel), and thenegative terminal of battery suorce 31, in the aforementioned sequence.The embodiment of FIG. 5, in accordance with the principles of thepresent invention, is thus seen to comprise an astable oscillatorcircuit utilizing an NPN transistor 24 and a PNP transistor 25 as thecontrolling transistor including a diode 30 connected across theterminals of driving coil 12 in order to absorb the energy which isstored in driving coil 12 which is generated at the lagging edge of thedriving coil pulse.

In the oscillator circuit of FIG. 5, since it comprises an astablecircuit it will oscillate even when balance wheel 1 is not oscillatingto provide an output pulse to driving coil 12 having a particular pulsewidth. If this output pulse is suflicient to overcome the peak ofpotential energy shown in FIG. 3, as discussed above, to providesufficient energy to anchor 6, the amplitude of oscillation of thebalance wheel will be increased, resulting in an induced voltagegenerated in driving coil 12 and detecting coil 13. Since in theembodiment of FIG. 5, the oscillator circuit is arranged so that thevoltage induced across terminals 12a and 12b is added to the inducedvoltage in detecting coil 13, this induced voltage will bring transistor24 to the conductive state more stably even before controllingtransistor 25 is switched on, to provide an electrical pulse to drivingcoil 12 to add more force to the balance wheel. Thus, the oscillatorcircuit of FIG. synchronizes its pulse output with the oscillatingperiod of the balance wheel, thereby adding energy to the balance wheel.

The oscillator of the present invention, shown in FIG. 5, is thus seento be advantageous over the conventional oscillator such as thatdepicted in FIG. 4 in the following manner. The oscillator of FIG. 5generates an electrical pulse of sufficient width at the start of thebalance wheel oscillation which is independent of the amplitude of thebalance wheel oscillation; and when the balance wheel attains aparticular amplitude, the width of the generated electrical pulsebecoming narrower to become a function of the amplitude of the balancewheel oscillation. Thus, in the conventional oscillator arrangement asshown in FIG. 4, the electrical pulse width is equal to the chargingtime which is determined by charging condenser 18 and resistor 19 whichis substantially constant, whereas in the oscillator circuit of thepresent invention as shown in FIG. 5, the sufliciently long chargingtime of the charging capacitor at the start of the balance oscillationdetermines the width of the output pulse which in turn is controlled bythe induced voltage generated in the detecting coil which is inserted inthe charging circuit of the charging capacitor when the amplitude of thebalance wheel oscillation is increased.

The following is a description of the action of the electromotive forcewhich tends to charge capacitor 26, after conduction, in the oscillatorcircuit of FIG. 5. When driving transistor 24 is saturated afterconduction of the circuit, the voltage on 12b may be represented by0:15, where E is the voltage of battery source 31, and a is the ratio ofthe number of windings between terminals 12a and 120 to the number ofwindings (i.e. winding resistance) between terminals 12b and 120.Accordingly the electromotive force which tends to charge capacitor 26is the sum of the difference between the voltage E of the power source31 and the voltage dB at terminal 12b, the relationship being given byEquation 1 below, wherein V is the induced voltage on detecting coil 13,and the voltage generated in the detecting coil by virtue of the mutualinductance with driving coil 12 being Vm.

The impedance Z as seen from both ends of charging condenser 26 when thecircuit of FIG. 5 is on, comprises with a combined inductance of drivingcoil 12 and detecting coil 13, the resistance of the coil winding wire,resistor 27, saturation resistance of the collector to emitter path ofdriving transistor 24, and the saturation resistance between the base toemitter path of controlling transistor 25. However, if the value ofresistor 27 is larger than that of the other impedances, the impedance Zwill be substantially resistive and approximately equal to R.Furthermore, if Zm is not too large than the expression a'E+Vml may beconsidered constant during the duration of the electrical pulse. Vm isgenerated by the mutual inductance of the driving coil and the detectingcoil, but in the transducer as illustrated in FIG. 1, the magnetic yokecircuit is opened in a portion thereof, and accordingly the inductanceis extremely small. Accordingly, at the start of the balance oscillationwhen the induced voltage is not generated, the charging voltage V andcurrent through capacitor 26 may be represented by Formulas 2 and 3 asfollows.

I I R where C is the capacitance of capacitor 26 and t being thecharging time.

The above Equations 2 and 3 are graphically depicted by curves A inFIGS. 10A and 10B. As indicated by Equations 2 and 3 above, the chargingtime constant is approximately RC. Since the charging current throughcapacitor 26 causes controlling transistor 25 to be switched on if thevalue of resistor 27 is increased, the charging time constant willbecome longer, and it will thereby be possible to maintain thecontrolling transistor 25 in the on state for a long period of time,whereby driving transistor 24 can supply a sufficiently wide pulse todriving coil 12. Initially the pulse width is increased in order toincrease the amplitude of the balance oscillation to the desiredamplitude, but as the balance oscillation amplitude increases, theinduced voltage will also increase, and the controlling transistor 25will be triggered even before the conduction period due to the timeconstant and the electrical circuit can be synchronized with the balanceoscillation period.

Furthermore, when the induced voltage is generated, the charge on thecharging condenser varies, i.e. the final voltage charge on chargingcondenser 26 changes from ociE-I-VITL to oc'E+ Vm+V, and when theinduced voltage is removed, the charge on charging condenser 26 returnsto the value of ot'E-l- Vm. Since the increase in the balanceoscillation amplitude causes an increase in the charging current, thecharging voltage will rapidly increase, to shorten the time required toreach the final voltage uE+ Vm. Accordingly, the charging current willrapidly decay, and the conduction time of controlling transistor 25 willbe reduced, since the charging current is the base current ofcontrolling transistor 25, and the pulse width will accordingly becomenarrower. Thus, if the induced voltage becomes large as compared withoc'E+ Vm, charging capacitor 26 is already charged to u'E+ Vm when V isremoved, the charging will immediately stop, for the final chargingvoltage is oc'E+ Vm, and the pulse width will be narrowed. Since thewidth of the induced voltage pulse is approximately equal to the timethat anchor 4 and balance wheel 1 are in engagement, and the pulse widthof the pulse applied to driving coil 12 is controlled as to be equal tothe width of the aforementioned induced voltage pulse, when balancewheel 1 reaches its amplitude corresponding to the final voltage, theadditional force to balance wheel 1 may be added most effectively.Conversely, in the event that the amplitude of the balance oscillationis reduced due to an outer disturbance, as the induced voltage isreduced, the pulse Width of the electrical pulse is widened, and thisaction tends to restore the original amplitude. Thus, in the embodimentof FIG. 5 of the present invention, the charging time of chargingcondenser 26 is a function of the amplitude of the balance oscillation.

Referring to FIGS. 10A and 10B, the variation of the charging voltageand current when the induced voltage V is generated is shown by curvesB, wherein the pulse width varies from to to too, where t loo.

Referring to FIGS. 9B and 9C, the dotted line curves therein correspondto the state wherein there is little or no induced voltage as indicatedby the dotted line curve in FIG. 9A. In the stable state of oscillation,the balance oscillation, the balance oscillation amplitude is large, andin the case that the induced voltage is large, as shown by the solidline curve of FIG. 9A, the pulse width of the voltage on the base ofcontrolling transistor 25, and that of the voltage on the collector erdriving transistor 24, ie the electrical pulse width, becomes narroweras shown by the solid line in FIGS. 9B and 9C.

Furthermore, curve C in FIG. 9B, and curve D of FIG. 9C are variationsof the induced voltage b caused by the motion of the balance wheel,wherein in FIG. 9A oc"=1.

Intermediate terminal 120 is provided in order to permit the variationof the pulse width by making the induced voltage V comparable with aE+Vm based on the condition that the voltage of the power source is a'E.If the voltage of power source 31 is very low, the same effect may beobtained when terminal 13a of detecting coil 13 is connected directly tothe collector of driving transistor 24.

In FIG. 6, there is shown a second embodiment of an oscillator inaccordance with the principles of the present invention, which is ofsimilar configuration to the arrangement of FIG. 5, with the exceptionthat the detecting coil 13 is connected between the emitter ofcontrolling transistor 25 and the positive terminal of battery source31. Accordingly waveform of the voltage on the base of the controllingtransistor 25 as shown in FIG. 9C is slightly modified, While retainingthe same charging characteristic for charging capacitor 26.

FIG. 7 illustrates a third embodiment of the present invention, which issubstantially similar to the arrangement of FIGS. and 6, with theelectromotive forces which provide the charge for charging capacitor 26being essentially similar to those in FIGS. 5 and 6, with the exceptionthat the electromotive force due to the voltage E of battery source 31is not uE but rather aE.

Referring to FIG. 8, there is shown a fourth embodiment of an oscillatorin accordance with the principles of the present invention, which is inmany respects similar to the previously described embodiments of FIGS.57 with the exception that detecting coil 13 is connected tointermediate terminal 12b and the emitter of controlling transistor 25,but otherwise remains essentially similar to the above describedembodiments of FIGS. 57.

In the embodiment of FIGS. 58, the charging resistor 27 has the samecontrolling effect since it is not in series with the group comprisingbattery source 31, driving coil 12 and the collector to emitter path ofdriving transistor 24.

Thus, as shown above, the oscillators of FIGS. 58, in accordance withthe principles of the present invention, provide an electric time piecewhich may be self excited even when it is necessary to overcome a largepeak of potential energy, as shown in FIG. 3 in order to maintain thebalance oscillation, wherein the amplitude of the balance oscillation isautomatically controlled, and where the power consumption in the stablestate of oscillation is substantially decreased.

It is understood that, although the oscillators of the presentinvention, which have been described in conjunction with theelectromechanical transducer of FIG. 1, are not limited in applicationthereto, but are also adaptable for use in other electromechanicaltransducers for time pieces which must overcome a peak of potentialenergy at the start of the oscillation. Furthermore, although an NPNtransistor was shown as the driving transistor, and a PNP transistorshown as the controlling transistor, in the embodiments of FIGS. 58, itis understood that the transistor types may be reversed.

What is claimed:

1. An electric timepiece comprising a rotatably mounted, oscillatablebalance wheel; electro-mechanical transducer means for driving saidbalance wheel, said electro-mechanical transducer means includingmechanical means engaging said balance wheel in the region of the centerof the oscillatory path of said balance wheel for applying rotativeforce to said balance wheel and for displacement in response to therotative motion of said balance wheel, and magnetic circuit means forapplying displacing force to said mechanical means in response to apulse of magnetic flux applied thereto for driving said balance wheel,and for having a magnetic flux induced therein in response to thedisplacement of said mechanical means responding to the rotative motionof said balance wheel; and a stable oscillator circuit means having adriving coil in the output of said oscillator circuit means, coupledwith said magnetic circuit means to impart said pulse of magnetic fluxthereto in response to the output of said oscillator, charging circuitmeans for controlling the period of oscillation of said oscillator, anda detecting coil coupled with said magnetic circuit means for generatinga detecting voltage in response to said induced flux and disposed inseries connection with said charging circuit means with the polarity ofsaid induced voltage such that the pulse width of said displacing fluxapplied to said magnetic circuit means by said driving coil narrows assaid detecting voltage increases.

2. An electric timepiece as defined in claim 1, wherein said oscillatorcircuit includes a driving transistor having said driving coil seriallyconnected to its collector; a controlling transistor; and a couplingresistor interconnecting the collector of said controlling transistor tothe base of said driving transistor, said charging circuit meansincluding a charging capacitor and a charging resistor in seriesarrangement.

3. An electric timepiece as defined in claim 2, wherein said drivingcoil has a pair of end terminals and an intermediate terminal, saiddetecting coil having a pair of end terminals, said detecting coil endterminals serially interconnecting said driving coil intermediateterminal and said charging circuit means, the other end of said chargingcircuit means being connected to the base of said controllingtransistor, said driving coil end terminals being connected respectivelyto the collector of said driving transistor and the emitter of saidcontrolling transistor.

4. An electric timepiece as defined in claim 2, wherein said drivingcoil has a pair of end terminals and an intermediate terminal, saidcharging circuit means interconnecting said driving coil intermediateterminal and the base of said controlling transistor, one of saiddriving coil end terminals being connected to the collector of saiddriving transistor, said detecting coil interconnecting said controllingtransistor emitter and the other of said driving coil end terminals.

5. An electric timepiece as defined in claim 2, wherein said drivingcoil has an intermediate terminal connected to the emitter of saidcontrolling transistor, said 1 1 l 2 detecting coil and charging circuitmeans being in series References Cited connection interconnecting thecollector of said driving UNITED STATES PATENTS transistor and the baseof said controlling transistor.

6. An electric timepiece as defined in claim 2, said driv- 2,986,6835/1961 Lau et a1 58-23 ing coil having an intermediate terminal, saidcharging circuit means interconnecting the collector of said driving 5RICHARD WILKINSON Primary Exammer transistor and the base of saidcontrolling transistor, 5 C S O S Assistant Examiner said detecting coilinterconnecting the emitter of said controlling transistor and saiddriving coil intermediate ter- US, Cl, X R

minal. 318-129

